Molecular engineering of microporous crystals: (III) the influence of water content on the crystallization of microporous aluminophosphate AlPO 4-11

Bin Zhang, Jun Xu, Fengtao Fan, Qiang Guo, Xiaoqiang Tong, Wenfu Yan, Jihong Yu, Feng Deng, Can Li, Ruren Xu

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38 Scopus citations

Abstract

The influence of water content on the crystallization of the microporous aluminophosphate AlPO4-11 was investigated by a combination of in situ UV Raman and ex situ XRD and NMR characterizations. Under high water content conditions (Al2O3:H2O = 1:20-69), an AlPO4-5 intermediated formed first and later co-existed with AlPO4-11. In the last stage of crystallization, the crystalline AlPO4-5 completely disappeared and well-crystallized AlPO 4-11 was obtained. The position of the three signals observed in the 31P MAS NMR spectra of the isolated solid samples did not change during the hydrothermal treatment, suggesting that the fragments containing the P site in the junction of 6- and 4-membered rings of both AlPO4-5 and AlPO4-11 formed first and that the environments of the P sites were very similar to those in the final structure. A significant increase of Al concentration in liquid media was observed before the appearance of XRD detectable AlPO4-11. Under low water content conditions (Al 2O3:H2O = 1:15), the AlPO4-11 was directly crystallized from the initial mixture. In situ Raman spectra showed that the 10-membered rings were complete by the time the transformation of octahedral Al to tetrahedral Al was finished and that the conformation of the protonated di-(i-propyl)amine changed little during the crystallization. The present study showed that the composition of the liquid phase is critical to the formation of a specific structure.

Original languageEnglish (US)
Pages (from-to)212-221
Number of pages10
JournalMicroporous and Mesoporous Materials
Volume147
Issue number1
DOIs
StatePublished - Jan 1 2012

Keywords

  • AEL
  • AlPO-11
  • Aluminophosphate
  • Crystallization
  • Zeolite

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